Building Acoustic Measurements

Navcon Engineering has conducted several surveys to verify the acoustic quality of new constructions.  The acoustic measurement surveys typically include the measurement of the sound transmission of party walls or party ceilings, the impact isolation of ceiling/floors, the entry doors or exterior walls.

The assessment of the sound isolation of rooms is based upon ANSI standards defining the test methodology and evaluation curves.   The Sound Transmission Class (STC) is a single-number used to rate the ability of a partition to reduce sounds or noise passing from one room to another. Typically the STC is measured in an acoustical laboratory under controlled test conditions.  The test requires an excitation room with a sound source and a receiver room.  The noise reduction is the difference between the averaged sound pressure levels in each room.  By correcting the absorption/reverberation effect of the receiving room the results are normalized to the size of the partition.

The Field Sound Transmission Class (FSTC) is essentially the same as STC rating except that it is measured in the field. The FSTC is used to quantify the actual as-built partition transmission loss across the frequency range of interest and incorporates corrections for the sound absorption in the receiving room.  In some measurement environments the correction of the sound absorption may not be adequate due to the size of the room or the partition under test.  In those case the field testing would not correct for the sound absorption of the receiving room and only document the noise reduction between the two sides.  The noise reduction can be assess in terms of the Noise Isolation Class (NIC).

The Impact Insulation Class (IIC), is a single-number measure of a floor/ceiling assembly’s resistance to the transmission of structure borne impact noise. Sometimes referred to as Impact Isolation Class, the IIC is determined based upon a normalized one-third octave band sound pressure spectrum centered between 100 to 3150 Hz.

Field Impact Insulation Class (FIIC) is similar to the IIC. The FIIC is determined by exciting the floor in a source room using a ISO certified floor tapping machine, measuring the resulting sound pressure spectra in the receiving room and then applying a normalized sound pressure spectrum (per the ASTM standard).

The Floor Tapping Machine is exciting the tile floor.  The sound pressure levels is measured in the adjacent condos/rooms and condos/rooms below.  The sound level in the receiving rooms are corrected for the absorption.

Field Impact Insulation Class:  A tapping machine is used to excite the floor.  The sound level (Lp) and the reverberation time in the receiving room are measured.  The averaged 1/3 octave band sound levels from 100 Hz to 3,150 Hz are corrected for the room characteristics (reverberation).  A reference curve is adjusted along the measured data so that the maximum deviation between the measurement data (Ln) above the contour line is smaller than 8 dB and the sum of all deviations is less than 32 dB. The data shows a FIIC of 62 (Note: 62 = 110 - 48  -> Contour Value at 500 Hz)
Field Sound Transmission Class:  A speaker is placed in the corner of the source room.  The average sound level in the source room (L1) and the average sound level in the receiver room (L2) and the reverberation time in the receiver room are measured.  The frequency of interest is from 125 Hz to 4,000 Hz.  The transmission loss is calculated as a difference between the source and receiver room levels with an additional correction for the receiver room characteristics (reverberation) and the size of the common wall or ceiling.  A reference curve is adjusted along the measured data so that the maximum deviation between the measurement data (FTL) below the contour line is smaller than 8 dB and the sum of all deviations is less than 32 dB. The data shows a FSTC of 46 (Note: 46  -> Contour Value at 500 Hz)

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Last modified: May 25, 2007